Endon Bharata

Compressive Stepped-Frequency Continuous-Wave Ground-Penetrating Radar

Data acquisition speed is an inherent problem of stepped-frequency continuous-wave (SFCW) radars, which may discourage further usage and development of this technology. We propose an emerging paradigm called compressed sensing (CS) to overcome this problem. In CS, a signal can be reconstructed exactly based on only a few samples below the Nyquist rate. Accordingly, the data acquisition speed can be increased significantly. A novel design of an SFCW ground-penetrating radar (GPR) with high acquisition speed is proposed and evaluated. Simulation by a monocycle waveform and actual measurement by a vector network analyzer at a GPR test range indicate the applicability of the proposed system.

A Modified Bow-Tie Antenna for Improved Pulse Radiation

The analysis, design, and realization of a modified bow-tie antenna optimized for impulse ground penetrating radar (GPR) applications is described. The proposed antenna shows improved properties important for GPR, which include its compact size (in comparison with a conventional bow-tie antenna) and ability to radiate UWB pulses with increased amplitude and very small late-time ringing. A substantial increase in the amplitude of the transmitted pulse is achieved by utilizing radiation from discontinuities introduced by the resistive loading employed in the antenna to suppress late-time ringing. By choosing an optimal distance between the antennas feed point and the location of the resistive loading, radiations that occur from the antennas feed point and the mentioned discontinuities at the resistive loading will combine constructively in the boreside direction of the antenna. As a result, one will observe a substantial increase of the amplitude of the transmitted pulse in the boreside direction. Furthermore, an analytical expression describing approximate time-harmonic current distribution is derived to indicate an optimal resistive loading profile for the proposed antenna. Additionally, the traveling-wave current distribution of the antenna is theoretically analyzed to examine the applicability of the obtained time-harmonic expression for pulse excitation. It has been found that when the antenna is resistively loaded both the time-harmonic and traveling-wave currents decay to approach nearly the same value at the end section of the antenna. As the amount of current at the antenna ends corresponds to the level of reflection which occurs there, the derived expression is found to be useful to indicate an optimal loading profile for the proposed antenna. A theoretical model of the proposed antenna has been developed to perform numerical analysis using a modified NEC-2 code. In addition, an experimental verification has been carried out and both the simulation and experiment confirmed the improved properties of the proposed antenna.

Improved Bow-Tie Antenna for Pulse Radiation and Its Implementation in a GPR Survey

In our previous works we developed an improved UWB bow-tie antenna for high-resolution GPR applications. The antenna has been designed to detect small shallow-buried objects for which it should be able to transmit short pulses with very small late-time ringing. It has been shown theoretically that in comparison with conventional bow-tie or dipole antennas, this antenna radiates significantly stronger pulses in its broadside direction with very small late-time ringing. In this paper, experimentally we compare the antenna with a resistively-loaded planar dipole which is commonly used for GPR. It has been found that the antenna exhibits superior characteristics in terms of significantly larger amplitude of the transmitted pulses and much smaller late-time ringing. Furthermore, the antenna has been implemented in a commercial GPR system and tested in real GPR surveys. In this paper we demonstrate that the implementation of this antenna results in clear B-scan images which allow one to easily observe the detail of the shallow subsurface.

Characterization of 4×4 high gain microstrip array antenna for 3.3GHz WiMAX application

This paper presents the design of microstrip array antenna for 3.3GHz WiMAX (Worldwide Interoperability Mobile Access) application. The proposed antenna comprises of 16 rectangular patches with microstrip line feeding network established using a quarter-wavelength transformer impedance matching technique. To avoid grating lobes affected by the spacing between patches, the patch separation to the adjacent patches is set to be 0.6 of wavelength. Hence, in order to achieve high gain required by the WiMAX specifications, the array consisted of 16 patches is applied where the patches are structured in 4×4 (columns x rows) formation. The antenna structure is then deployed on an Arlon DiClad 527 substrate which the thickness, dielectric constant and loss tangent are 1.6mm, 2.5 and 0.0022, respectively. The characterization result of return loss, VSWR (Voltage Standing Wave Ratio), radiation pattern, and gain are presented consecutively. From the result, it shows that the proposed antenna has the overall gain of 16.02dB and the return loss of 29.85dB that corresponds to VSWR of 1.07 at center frequency of 3.35GHz, whilst the working bandwidth is 150MHz ranges from 3.25–3.40GHz.

Bent tapered microstrip balun transformer

In this paper the traditional tapered microstrip balun transformer is modified by bending its whole structure to significantly reduce its length. The resulting bent tapered microstrip balun is then extended with a twin-semirigid line to simplify antenna feeding. The decoupling coefficient of the proposed balun has been found to be smaller than ™30 dB.

Theoretical and Experimental Analysis of a Rolled-Dipole Antenna for Low-Resolution GPR

In this paper a rolled dipole antenna for low-resolution impulse ground penetrating radar (GPR) is theoretically and experimentally investigated. The antenna has been designed for transmission of monocycle pulses with duration of 5 ns (200 MHz central frequency) suitable for low-resolution GPR applications. The dipole is rolled to considerably reduce its length and resistive loading with the Wu-King profile is applied for suppression of late-time ringing, important for GPR. It is shown theoretically that the antenna radiates the pulse with no late-time ringing. Furthermore, by rolling the wires the antenna length is reduced by a factor of 4 with no evident negative impact on the antennas characteristics. A shield for the antenna has been designed, constructed and integrated with the antenna. Furthermore, it has been found that a tapered bow tie can be combined with the antenna in such a way that a significant increase in the antenna efficiency is obtained, resulting in a unique hybrid of a dipole and a bow-tie antenna.

Rolled Dipole Antenna for Low-resolution GPR

In this paper a rolled dipole antenna for low-resolution impulse ground penetrating radar (GPR) is theoretically investigated. The antenna is designed for transmission of monocycle pulses with duration of 5ns (200MHz central frequency) suitable for low-resolution GPR appli- cations. The dipole is rolled to considerably reduce it length and resistive loading with Wu-King proflle is applied for suppression of late-time ringing important for GPR. Using NEC-2 as the numerical tool it is shown that the antenna radiates the pulse with no late-time ringing. Further- more, by rolling the wires the antenna length is reduced by a factor of 4 with no evident negative impact on the antennas characteristics.

Wideband printed dipole antenna fed using modified planar marchand balun

In this paper, the development of wideband printed dipole antenna which is fed using modified planar Marchand balanced-unbalanced (balun) circuit is presented. The antenna is intended to operate at frequency of 3.3GHz with wideband response for wireless application. A modified planar Marchand balun is chosen to transform an unbalanced circuit of coaxial input to a balanced circuit of printed dipole antenna. The choice of Marchand balun type is due to its characteristics such as low loss, wide bandwidth response, and easy for planar structure implementation. The proposed antenna is implemented on a 1.6mm thick Arlon Diclad 527 dielectric substrate. The experimental characterization shows that the realized antenna has the bandwidth response of 600MHz for voltage standing wave ratio (VSWR) ≤2 ranges from the frequency of 3GHz–3.6GHz with the gain achievement of 5.69dBi–5.85dBi for the frequency range of 3.3GHz–3.4GHz.

A ground penetrating radar antenna with improved shield

In this paper, development of an improved antenna for short-range ground penetrating radar (GPR) applications s discussed. the antenna improvement is obtained in the form of increased radiation efficiency and reduced dimension. In addition, an improved metallic shield has been designed not only for protection against EMI and antenna coupling, but also for strengthening radiation into the ground.